you should be backing up all devices with removable storage or not, SSDs can also die without warning.
My macbook updates my documents etc to my NAS, and the NAS syncs to crucial folders to the cloud (not everything for cost reasons)
You should always assume your device can be stolen, you can spill fluids on it (or a guest), a cat can pee on it, an electric shock may kill it... No matter how great care you take of it, shit happens, data needs to be safe.
The SSD dying standalone vs the system dying doesn't change at all for data security. It's not a different risk factor
I wouldn't choose to buy a car I use every day that's 100x less reliable than a normal car.
If your looking for arguments against soldered storage the facts ssds are wear items and will eventually need replacement is a much better one.
If given a choice, I prefer a system where a HDD/RAM/GPU/CPU/PSU/Screen/Port/Battery/Keyboard failure is barely if at all disruptive to one where all of these effectively brick the system.
... single point of failure. /s
The point is it shouldn’t matter if the cpu or ssd dies because you have backed up everything already and are prepared for anything to fail or happen to the device rather then “oh the ssd is removable so in these select few situations I can recover my data”